1. Field of the Invention
The present invention relates to an image forming device such as a color laser printer, and a process cartridge mounted in the image forming device.
2. Description of Related Art
Conventional image forming devices such as laser printers normally include a process cartridge detachably mounted in the image forming device. The process cartridge includes a developing roller for bearing toner, and a photosensitive drum disposed in opposition to the developing roller. Electrostatic latent images are formed on the surface of the photosensitive drum.
In the developing process, a bias is applied to the developing roller, supplying toner from the developing roller to the photosensitive drum. The supplied toner develops an electrostatic latent image that has been formed on the photosensitive drum, producing a toner image thereon.
Subsequently, the toner carried on the photosensitive drum is transferred onto paper, forming an image on the paper.
It is known that as toner is consumed in these types of image forming devices, transmission density (base 10 logarithm of the inverse of the transmittance) of the toner image formed on the paper generally increases.
For this reason, as disclosed in Japanese patent-application publication No. HEI-9-311510, a technology for stabilizing changes in the density of a printed image has been proposed. In this technology, developing bias values that are optimal for various ambient temperatures and humidity, the accumulated number of sheets developed by developing devices, and the like are stored in a developing bias memory. The optimal developing biases for the conditions of use are read from the developing bias memory to control the power supply of the developing device according to the developing bias value.